If you're asking how a 16' toon will handle big water, you probably shouldn't consider one. They handle like a beach toy. Basically, they don't handle....
mpilot hit on a point that's important in my experience. These little guys will try stuffing their noses into about every other wave, where a longer boat would span the distance between wave crests much easier, providing superior handling. If swells are involved, all bets are off. You want a different style boat......
If I were trailering exclusively, I think there are advantages to a 20-22 foot boat when loading and unloading, especially if doing that by yourself. If frequent trailering is not a factor, I'd go 24'.
A 50 on either size boat is fine for cruising. In Mich. you'll see the vast majority of pontoons equipped with something like that. If you're plans include pulling anything, your plans should include doubling that power at minimum.